1. Technical Field
The present invention relates to an apparatus which controls the scanning of a sample or body by a scanning probe system, the processing of the signals measured, and the pre-processing for storing such signals on a conventional video recorder.
2. Prior Art
The expression `Scanning probe system` will hereinafter be used as synonym for all kind of measurement or investigation systems, be it for medical or non-medical purposes, that have a probe for the determination of certain parameters of a sample. The word sample means in this connection any kind of material to be investigated. This is not limited to pure scientific samples such as semiconductors, metals, polymers, tissues, cells, and bacteria. It is also meant to cover human and animal bodies. In such a scanning probe system, the probe runs over the sample to be investigated in a step like manner, as is for example known from computer spin tomography systems, positron emission tomography systems, microtomography systems x-ray systems, scanning tunneling microscope systems, scanning electron microscope systems and so forth. The scan movement of the probe with respect to the sample is not necessarily a translatory movement. There are also systems known that scan a sample by means of a rotational movement of the probe around the sample to be investigated.
In the following, the present invention will be described in detail in connection with scanning probe microscope systems for the sake of simplicity.
The scanning probe microscope techniques evolved from the Scanning Tunneling Microscope (STM) developed by G. Binnig and H. Rohrer in 1982. The STM, which is disclosed for example in the U.S. Pat. No. 4,343,993, led to the development of a huge variety of microscopes. These microscopes are designed to investigate surfaces and atoms, or molecules on top of them, with atomic resolution from 100 nm down to about 0.1 nm. A common feature of scanning probe microscope systems is a fine tip, also more generally referred to as probe, with a very small radius of curvature at its apex. The probe is scanned over the surface of a sample by using positioning units.
Some scanning probe techniques are also based on the Atomic Force Microscope (AFM) which was invented by G. Binnig in 1986 (U.S. Pat. No. 4,724,318) and which has been further developed since then. Images of magnetic domains have been obtain by Magnetic Force Microscopy (MFM), as for example described by H. J. Mamin et al. in Applied Physics Letters, Vol. 55 (1989), pp. 318ff. A Scanning Capacitance Microscope is known from the patent U.S. Pat. No. 5,065,103, a Scanning Acoustic Microscope from U.S. Pat. No. 4,646,573, and a Scanning Thermal Profiler from U.S. Pat. No. 4,747,698. The scanning probe microscope techniques are also used in light microscopes having a resolution not limited by diffraction. In these so-called Scanning Near-field Optical Microscopes (SNOMs), described for example in U.S. Pat. No. 4,604,520, the probe essentially consist of a waveguide for light waves ending in a tiny aperture which either receives or emits light within the proximity of the surface of a sample. For the purpose of this invention, all these systems are referred to as scanning probe microscopes (SPMs).
SPMs are in principle simple to implement and provide for extreme resolutions. This is one of the reasons why SPMs are now widely employed when dealing with all kinds of surface analysis and imaging of sub-microscopic phenomena. In the past, SPMs were mostly used for scientific applications. The SPM techniques have to date also found their technical application for example in high technology manufacturing and quality control processes.
Under certain preconditions, SPMs could become more important outside basic science and highly specialized, industrial environments, too. The main factors are cost and complexity of SPM systems which typically include data processing, data acquisition and scan control means. In todays SPM systems, usually expensive hard disks or magneto optic storage disks and specially programmed personal computers are employed. Examples of conventional data acquisition and control systems are given in the article "Data acquisition and control system for molecule and atom-resolved tunneling spectroscopy", E. I. Altman et al., Rev. Sci. Instrum., Vol. 64, No. 5, May 1993, pp. 1239-1243, and in the article "Scan control and data acquisition for bidirectional force microscopy", D Brodbeck at el., Ultramicroscopy, Vol. 42-44, 1992, pp. 1580-1584, North Holland. Both systems, described in the above articles, are computer controlled systems comprising hardware interfaces, a 386-microprocessor based personal computer and specially written software. These kind of systems have to cope with difficulties concerning processing speed as for example described in Section D, with title "Computer system", of the E. I. Altman's article. Even when using assembly language for the program which controls data acquisition and processing the maximum sampling rate that can be achieved is in the range of 150000 samples per second only. There is a demand for systems with faster data collection speed. In addition, the system described by E. I. Altman et al. relies on the access to a fast data storage space. Special software is needed to access extended memory locations beyond the range normally accessible. Such an extended memory is usually small and an additional storage medium for storing complete scans is required. It is an important disadvantage of these systems that the images obtained and afterwards stored in a computer or peripheral memory are gray scale images with a resolution of 8 bits. From this short section giving an overview of existing data acquisition and control systems it is obvious that there are some inherent drawbacks.
Document EP-A-0469274 is an example of such a system. It discloses an ultrasonic inspection and imaging instrument in which, when parts of the same kind are inspected, proper measurements conditions can readily be set to ensure that inspection efficiency is improved. The electrical signal generated by a probe and representing the echo obtained from an object under examination is amplified and fed to a peak detection circuit. The peak value so detected is converted into a digital value and sent as input data onto the bus of a microprocessor unit further equipped with a memory and a display. The measurement data is manipulated in the processor unit according to programs stored in the memory so as to allow reduced image examples to be displayed to, and become modifiable by, an operator.
In case of medical systems, the scan process and data acquisition is usually controlled by the computer. Due to the huge amount of data to be processed and stored, expensive computer systems with high density storage media are employed. To cope with the high speed data acquisition, the storage media are used in these systems have to be very fast. In addition, the resolution of images obtained is only 8 bit.
Document WO-A-85/02105 discloses an ultrasound diagnostic apparatus for displaying two-dimensional blood flow information superimposed over anatomical information on a video display. The apparatus includes a transducer array for transmitting a series of ultrasound bursts toward the area of the patient in which blood flow information is desired. The ultrasound is transmitted in a plurality of directions so as to achieve a sector scan. Ultrasound reflected from the blood is received by the transducer array and converted to corresponding electrical signals. Frequency differences between transmitted and received ultrasound are fed, in digital form, to a processor unit which computes velocity estimators. The signals generated by the processor unit are coupled to a display such as a color television monitor via a scan converter memory which also receives anatomical information derived from the analog signal produced by the transducer array. The document does not address the problem of improving the data acquisition speed and image resolution in an x-y positioning scanning probe system.
Other examples of the art, in the field of microscopes, can be found in documents U.S. Pat. No. 5,212,383, which discloses a scanning electron microscope in which electrons with positional differences are detected by detectors arranged around the specimen under examination and such positional differences are converted into signals for synthesizing color on a video display, and U.S. Pat. No. 4,398,211 which discloses a light microscope using a combination of charge-coupled photodiodes and a high-resolution lens to provide a representative high-resolution picture of an object on a display. In both documents any digital treatment of the data is conducted through a computer with its associated memory and programs and therefore suffers from the same drawbacks mentioned above.
For a further success of the scanning probe technique in whatever area, it is essential to replace the known data acquisition and control systems by faster ones, the quality (resolution) of the data stored being comparable or even improved. It would be furthermore of advantage if one could use a cheap storage medium for storing the huge amount of information. In particular the process control by means of software running on a computer and the data processing with computers have been identified as bottleneck as far data acquisition speed and scan (control) speed are concerned. A further disadvantage of conventional data acquisition systems is that the images obtained are stored with a resolution of only 8 bits. To date, one uses only 8 bit by storing gray scale images, as already mentioned above.
It is an object of this invention to provide for improved data acquisition, by means of Scanning Probe systems, and processing of the data obtained by such systems.
It is an object of this invention to provide for data acquisition and data processing with improved image resolution.
It is an object of this invention to provide for fast and efficient synchronization of the data acquisition/processing and the control of the scanning process.
It is another object of this invention to provide for a system which allows storage of scan data with resolution of more than eight bits.